Centrifugal pump casing relief system

ABSTRACT

In a fluid flow network including a centrifugal pump, a system and kit for monitoring said centrifugal pump and relieving the pump of fluid when the pump is operating at no-flow conditions. The system comprises a fluid conduit connected to the pump, at least one sensor for indicating when the pump is operating at no-flow conditions. The sensor is selected from the group consisting of: temperature sensors, pressure sensors, and motor current sensors. The system has a fluid control means located in the fluid conduit. An electric snap-action valve is included that has an inlet connected to the fluid conduit and an outlet and a diaphragm. The diaphragm is movable between a first position and a second position. A power supply is included.

RELATED APPLICATION

This application is a divisional of co-pending patent application Ser.No. 11/341,289 filed 27 Jan. 2006.

BACKGROUND OF THE INVENTION

The present invention relates to centrifugal pumps and, morespecifically, systems and devices to monitor operating parameters ofcentrifugal pumps to prevent damage to the centrifugal pumps.

Centrifugal pumps are relatively simple pumps used for fluid movementwithin piping systems. The pumps operate efficiently requiring only onemoving part. However, care must be taken to insure that the pump isbeing operated within proper parameters. Specifically, care must betaken to insure that the pump is not operating at a “no-flow” condition,which can lead to damage of the pump and burning out of the motordriving the pump.

If a centrifugal pump is operating at a “no-flow” situation, fluid flowwill have stopped through the pump. A small amount of fluid can remainin the pump and become trapped within the pump. This fluid will bechurned by the spinning impeller of the centrifugal pump. Because thereis only a small amount of fluid within the pump, the temperature of thefluid can increase quickly, and the fluid will begin to boil. Theboiling fluid will increase the pressure within the system. Theincreasing temperature and pressure feed off of each other, and thepressure can quickly increase to uncontrollable levels. Such increaseswill lead to damage to the piping system and the pump, such as damage tothe seals located at the joints, and the rise of the fluid temperaturecan lead to spontaneous tripping of “dry pipe valves” in fire protectionsystems. Other components, such as the pump seals, gauges, pressureswitches, valve packings, flow switches, etc., may also be damaged bythe pressure and temperature rise at no-flow situations.

Regulation of the pump is usually done by monitoring the pressure of thepump, the temperature of the fluid within the pump, or the electricalcurrent feeding the pump motor. Normally, a separate fluid path isprovided through the pump to assure a minimal flow of fluid to preventoverheating of the trapped fluids. Such a device to control the fluidflow is generally referred to as a casing relief valve.

The amount of time between the cessation of fluid flow through the pumpand the onset of damages depends on many factors, such as liquidtemperatures, the design and speed of the impellers located in the pump,fluid vapor pressure, and fluid volume in the volutes. Time before theonset of damages can range from over ten minutes to less than tenseconds, depending on the pump configuration. As the flow slows andstops within an operating pump, the pump parameters may change. Forinstance, the discharge pressure will rise, the motor current willdecrease, the fluid temperature rises, and the speed of the motor shaftincreases.

The discharge pressure of a centrifugal pump is a function of twosources: the inlet fluid pressure and any additional pressure added tothe inlet pressure by the pump, with the additional pressure beingdependent on fluid flow through the pump. Generally, centrifugal pumpsproduce the highest pressure rises or changes from the inlet pressure tothe discharge pressure at a zero flow rate (“no-flow”), or churncondition. The amount of additional pressure the pump contributesdecreases as flow increases through the pump.

If the inlet pressure changes, the discharge pressure will change by thesame amount. Several factors can lead to these fluctuations in pressure,including seasonal factors, number of pumps being employed, demand, andpipe size, to name a few. As an indicator for no-flow situations, oneshould monitor the difference between inlet and discharge pressure.

As noted above, the motor current also varies, with the current beingapproximately fifty percent of the full load at churn, to nearly onehundred percent of current load at full flow. Motor currents below acertain level can indicate little or no fluid flow through the pump.Motor currents of a running motor will fall below churn levels only ifthe fluid in the volutes flashes to vapor. Current levels are notaffected by either the inlet pressure or the fluid temperature, but canbe altered by variations in the voltage of the power source, with lowervoltages resulting in higher current levels.

Generally, it has been preferred to determine the temperature of thefluid with the use of a sensor device, such as a transducer or a switch,by placing the sensor directly into the fluids located in thecentrifugal pump. The fluid temperature is measured directly, and thesensor device can immediately and automatically adjust to temperaturechanges. Pressure or voltage changes do not alter the sensors. However,such sensors may have problems of reacting quickly enough for a rapidlyrising or falling temperature.

The most common packaging configuration for a centrifugal pump is tomount a “horizontal split case” pump and an electric motor on a commonsteel base plate. The drive shafts of the two devices are connectedusing a coupling that will allow for some mis-alignment between the pumpand the motor.

If the coupling is removed and the motor is then started, the motor willdraw approximately twenty percent of the maximum continuous current,commonly referred to a full load current. If the coupling is thenreinstalled and the pump restarted with the discharge valve closed, themotor will then draw approximately fifty-five percent of the full loadcurrent. The value of the current rises as flow is added to the pump byopening the discharge valve.

Centrifugal pumps are preferably driven by three-phase induction motors,commonly referred to as “squirrel cage” motors. Squirrel cage motors usea differential slip to allow for changes between the “synchronous” speed(usually 1800 RPM and 3600 RPM) and an operating speed that is typically25 to 100 RPM lower than the synchronous speed. As the mechanical loadchanges, the speed will change; a greater load equals a greater slip. Agreater slip means a higher rotor current for the pump, producing highertorques to drive the load, which translates into a higher flow throughthe pump. Devices that monitor the pump load are not generally commonlyused.

The present state of the art to prevent overheating in a pump uses acasing relief valve located on the discharge side of the pump. Fluidpumped through this valve may be discharged to a drain or recycled intoa fluid storage. Some relief valves may pump the fluid back into theinlet of the pump, which increases the potential for the pump tooverheat. Such devices use a mechanical pressure detector and aninternal valve to release fluids at churn conditions. The simplestdesign uses a plunger and a compressed helical spring to seal the valve.As pressure rises, the plunger is pushed backward, allowing fluid toflow through into the by-pass line of the valve. As pressure falls backto normal levels, the plunger will reseal the valve.

The described relief valve has some drawbacks. Since the valve isoperated by discharge pressure (as opposed to pressure differential) itmay not open at proper times. For instance, if the inlet pressure israther low, the spring and plunger may not activate, even if there is asignificant change in the pressure, since the outlet pressure may stillbe lower than the pressure necessary to activate the plunger. Likewise,the flow amount is a variable dependent on the differential between thepump discharge and the valve trip pressure. A lower discharge pressurerelates to a lower flow rate, which increases the possibility of pumpdamage. Also, the spacing between the valve and the plunger is basedupon the pressure differential. If the differential is low, the spacewill be small, which potentially may lead to small particles becomingentrapped between the plunger and the valve, which could prevent thevalve from being resealed. The result is a constant fluid leak, which,eventually, can lead to general failure of the valve,

While it has been known to monitor such variables to prevent pump damageor fatigue, to date there has been no simple arrangement to monitor upto all three of these variables within a single system. Thus, it wouldbe advantageous to develop a system that would monitor centrifugal pumpswhile minimizing problems that could lead to failure of the monitoringsystem and the pump.

SUMMARY OF THE INVENTION

Within a fluid flow network including a centrifugal pump, the presentinvention comprises a system and kit for monitoring the centrifugal pumpand relieving the pump of potentially damaging fluid when the pump isoperating at no-flow conditions. The system comprises a fluid conduitconnected to the pump, at least one sensor for indicating when the pumpis operating at no-flow conditions. The sensor is selected from thegroup consisting of: temperature sensors, pressure sensors, and motorcurrent sensors. The system has a fluid control means located in thefluid conduit. An electric snap-action valve, preferably a solenoidoperated valve, is included that has an inlet connected to the fluidconduit and an outlet and a diaphragm. The diaphragm is movable betweena first position and a second position. A power supply is included. Themethod of installing the system and/or kit is also included in thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a centrifugal pump arrangement accordingto the present invention installed in a piping system.

FIG. 2 is a perspective view of a possible fluid control valve accordingto the present invention.

FIG. 3 is a perspective view of an alternative fluid control deviceaccording to the present invention.

FIG. 4 is a perspective view of a temperature sensor used according tothe present invention.

FIG. 5 is an exploded view of a solenoid valve used according to thepresent invention.

FIG. 6 is a perspective, partially exploded, view of a possible powersupply configuration used with the present invention.

FIG. 7 is a perspective view showing an initial step of installing thepump regulator system of the present invention.

FIG. 8 is a perspective view showing a further step of installing thepump regulator system of the present invention.

FIG. 9 is another further step of installing the pump regulator systemof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention which may be embodied inother specific structures. While the preferred embodiment has beendescribed, the details may be changed without departing from theinvention, which is defined by the claims.

The present invention provides a pre-engineered set of components thataddresses the shortcomings of the prior art discussed above with respectto centrifugal pumps. The components are included as kit that will allowthe end user to easily install the components and efficiently monitorthe specific pump. The kit provides the basis for a method of monitoringthe centrifugal pump and providing relief for the pump when the internaltemperature and/or pressure of the pump reaches critical conditions, orthe sensor indicates that the temperature and/or pressure may reachcritical conditions. The components include 1) a valve, orifice, orother similar device to determine the volume of fluid flow that willflow through the pump; 2) a valve to regulate the fluid flow; 3) asensor to detect a specific variable when the pump is churning, with thevariables being either pressure, temperature, or motor current; and 4) ameans to allow the sensor to operate the fluid regulation valve. The kitmay also include various pipes, connectors, and other hardware to assistin installing the valves and sensors. Likewise, instructions may beincluded with the kit.

The present invention provides an easy to use, reliable, predictablesystem that will reduce problems associated with “no-flow” situationsthrough the centrifugal pumps. Whereas previous designs and arrangementsrequired the placing of components and piping in specific, fixedlocations due to mechanical constraints of the pump itself, the separatedetection and operation valves of the present invention allows the userto place the valves in locations where they would be most advantageous.The flexibility of installation maximizes the ability to monitor theoperation of the pump. Furthermore, the system does not need to interactwith other systems or components to operate, and may include a back-uppower source, if necessary. The components included in the kit do notrequire any special tooling or skilled labor to install.

FIG. 1 is a perspective view of a pump relief system 10. The system 10is showed installed in connection with a fluid flow network 12 (showngenerally in phantom), which employs a centrifugal pump. As is known inthe art, the system 10 is connected to a fluid conduit or flow path thatoperates independently from the normal fluid flow in the network 12.This allows the system 10 to provide fluid flow when problems arise withthe centrifugal pump, such as “no-flow” conditions, thereby preventingor minimizing potential damage to the centrifugal pump. The systemgenerally comprises a fluid flow device, which may be in the form of aconventional, manually operable gate valve 14; a solenoid operated fluidregulator valve 15, and a sensor 25, depicted as a temperature sensor 25in FIG. 1. As fluid passes through a fluid conduit or pipe 22 incommunication with the pump 12, the sensor 25 can individually monitorfluid flow conditions of the pump 12 as shown in FIG. 1, or it ispossible to include other sensors such as pressure or motor sensors thatcan work in tandem to provide more checks for the pump. It is understoodthat the fluid conduit 22 refers to the entire length of pipe used inconnection with the system 10, and should not be limited to a specificshape or arrangement. The present invention allows for several variousarrangements of the individual sensors.

Fluid Flow Control

FIG. 2 provides a perspective view of the fluid flow device 14, which,as shown, is generally referred to as a manually operable gate valve.The gate valve 14 is a simple mechanical device used for regulating thevolume of fluid flow through the system 10. A handle 24 is turned toeither increase or decrease fluid flow through an internal conduit 26,thereby regulating the amount of fluid passing through a centrifugalpump during churn conditions. The design of the gate valve 14 allows forwide adjustments of fluid flow.

FIG. 3 provides an alternative fluid flow device, commonly referred toas a pipe union 114. The pipe union 114 has an internal restrictor plate116 with a predetermined orifice 118 that regulates the amount of fluidpassing through the conduit 26. The pipe union 114 is preferablyconstructed of a first half 120 and a second half 122. The restrictorplate 116 is located between the first half 120 and the second half 122.The three pieces 116, 120, and 122 are held together with a threadedunion section 124. If necessary, the restrictor plate 116 can bereplaced with another plate having a differently sized orifice if theflow is determined to be lower or higher than necessary.

As FIGS. 2 and 3 show, various flow control devices may be used for thepresent invention and the present invention should not be limited to aspecific part or device.

Sensors

FIG. 4 shows a perspective view of the conventional, commonly available,temperature sensor 25. The sensor 25 comprises a probe 40 that will bedirectly inserted into the piping system, as will hereinafter bedescribed. An electrical connector 42 is attached to the top of theprobe 40, preferably permanently affixed to the probe 40. A threadedarea 44 area on the probe 40 allows the sensor 25 to be secured to thepipe 22, again as will be later described, and in connection with theviews of FIGS. 1, 7, and 8. The probe 40 must be in contact with fluidwithin the pipe 22 at or near the area very close to the area whereactual heat may be generated in the system. The sensor 25 should beinstalled relatively near the impeller of the pump, or the sensor 25will not accurately portray the temperature. The temperature sensorpreferably includes a switch that is fixed to operate at 140° F. (60°C.), which is a temperature similar to the discharge temperature of aresidential fluid heater, with a temperature differential for the sensorbeing fixed at approximately 15° F. (or an approximate range of 12°-18°F.). The sensor 25 preferably operates a pilot duty metallic switch (notshown).

While a temperature sensor 25 was generally discussed above, pressuresensors and motor current sensors could be used in place of thetemperature sensor, or may be used concurrently in a single system.Whichever type of sensor is used, it will operate on similar principles.The sensors are designed to complete an electrical circuit, allowing acurrent to flow from the power source to a solenoid valve coil, with thecircuit being activated when the sensor registers a predetermined valuefor the related variable.

As with the temperature sensor 25 described above, a conventionalpressure sensor (not shown) used in the system would preferably includea pilot duty metallic switch. The pressure sensor can be located andinstalled at any point in the piping 22 that is connected directly tothe pump's discharge. That is, there should be no check valves or otherdevices located directly between the sensor and the pump's discharge.The pressure sensor will also be adjusted for a particular installation.Preferably, the inlet pressure for the pressure sensor is constant,which will result in a constant discharge pressure from the system. Ifthe inlet pressure is variable, a pressure sensor must be adjustedaccordingly, to insure that the solenoid 18 operating the valve 15properly opens, even at relatively low pressures.

A motor current sensor as may be used in the present system, as willlater be described, is preferably a solid state electronics module, andusually installed within the motor control center.

Solenoid Operated Valves

FIG. 5 provides a partially exploded view of the solenoid operated valve15 used in the present invention. The solenoid 18 has a coil 19 foroperating the solenoid armature 21 that is arranged for separableelectrical connection with an electrical connector 20 to be mounted ontothe valve 15. The connector 20 is secured to an electrical cord 54,which is routed to a power supply 50 (see FIGS. 1 and 6).

The solenoid operated valve 15 is preferably a piloted diaphragmoperated device. The valve 15 controls the pressure as it passes adiaphragm 32. A carburetor 35 may be included with the valve 15 as apressure release. As the coil 19 is energized by means of the solenoidarmature 21, a diaphragm 74 is pulled towards the coil 30, whichprovides complete opening or closing of the valve 15. The valve 15 ispreferably a “snap action” valve.

Referring further to FIG. 5, the solenoid operated valve 15 can beeither a normally open or a normally closed valve. The valve 15comprises a top section 70 and a bottom section 72. A spring 76 providesresistance and is seated upon the diaphragm 74 to provide pressure forsecuring the diaphragm 74 in place. A normally open version of a valve15 allows fluid flow when the coil 19 is de-energized, whereas aselection of a normally closed valve 15 allows fluid flow when the coilis energized. Determination of which valve type to use generally isbased upon whether or not fluid should be flowing should there be apower outage.

Power Supply

FIG. 6 illustrates a power supply 50 used in the present invention. Thepower supply 50 houses a transformer 52. The power source 50 iselectrically connected to the solenoid 19 of the valve 15 and the sensor25 with standard electrical cords 54 (see FIG. 1). A motor currentsensor 56 (see FIG. 6) for monitoring the motor used with the pump 12may also be connected to the motor 55. The sensor 56 is preferablyself-powered by the flow of current (preferably a 2.5 amp minimum flow)through the sensor 56 to the motor (not shown). The sensor 56 isconnected to the output of the motor, preferably with a two-conductorcable, commonly known and used with electrical connections. The motorcurrent flow through the sensor 56 is preferably detected using aconventional current transformer 52, which is used to detect themagnetic field of the motor current. The sensor 56 will test for twoconditions: 1) whether or not the motor current is high enough to assurethat the motor is running, and 2) whether or not motor current is low,thereby indicating no fluid movement in the system. When the sensor 56indicates that the current is high enough to indicate that the motor isrunning and low enough to indicate that there is no fluid flow, theelectrical output of the sensor 56 is activated, thereby energizing thesolenoid valve 15.

Installation

FIGS. 7-9 show various stages of installing the system 10. In FIG. 7, afirst section of pipe 60, having a threaded conduit 62, is connected tothe pump 12. The threaded conduit 62 will receive the sensor 25, asshown in FIG. 1. A second section or sections 64 of pipe 22 connect thepipe section 60 to the gate valve 14, and a third pipe section 66connects the gate valve 14 to the solenoid valve 15. To insure properfluid flow, the gate valve 14 and the solenoid operated valve 15 arepreferably installed within 2 to 4 inches from one another. FIG. 8 showsthe connector 20 being secured to the coil 19 of the solenoid valve 15.In FIG. 9 there is shown a discharge section 68 of the pipe 22 connectedto the solenoid valve 15, and the sensor 25 being finally connected tothe system 10, as further shown in FIG. 1. The pipe section 68 may leadto a drain or connected to recirculate the fluid into the general pipingsystem.

FIGS. 7-9 show one possible way of installing the kit components andshould not be considered as limiting. For example, one possiblepreferable alternative way is to install the power supply, next thesensor or sensors and thereafter the valves. When starting theinstallation process, the system installer must be sure to verify thatall of the electrical connections are secure. After energizing theelectrical supply, the operator must slowly open the fluid supply to thesystem, which will properly pressurize the gate valve 14 and/or thesolenoid operated valve 15. The centrifugal pump should then be startedand allowed to run. When it has been determined the pump is runningproperly, the operator may adjust the individual sensor to the specificoperating conditions.

When installing the power supply 50, it is preferable to mount thesupply 50 on a freestanding vertical structure 59, with the orientationbeing as shown in FIG. 6. The supply 50 should be mounted at least 12inches off of the floor. Power should be turned off to the supply untilit has been established that the sensors and valves are properlyinstalled.

When installing the temperature sensor 25, any fluid pressure on thepump itself should be released before installation of the sensor 25. Thesensor 25 is then threaded into the pipe section. The sensor 25 shouldbe installed in an upright, vertical position. An electric connector 54is attached to the sensor 25 (see FIG. 4) and then routed to the powerpack 50 (see FIG. 1).

As previously stated, the system is tailored for an individual pump'sneeds. For example, the size of the fluid control valve 14 is determinedby the amount of fluid that is flowing through the system. It shouldalso be determined what variable the system will be monitoring so thatthe proper sensor will be included with the kit for the system. Thiswill be taken into account when deciding how no-flow conditions will bedetected in the system. An extra, back-up battery may be included in thesystem in case of power failure. Another factor to consider is whetherthe solenoid operated valve 15 will be open or closed if power fails forthe system.

The present invention provides a simple and easy to use method forproviding a fluid flow detector system for protection of a centrifugalpump. Essentially, the present invention allows for a custom made sensorsystem. It has not been previously contemplated to provide the end userwith such a system selected from a component kit. The invention allowsfor the end user to receive an easy to install system that is tailoredfor an individual's needs. Likewise, the end user can obtain a kitincluding selected temperature, pressure, or motor sensors, or acombination of all three. By providing an individual sensor togetherwith an individual solenoid valve, the present system will provide aresultant product that can monitor fluid flow through a centrifugal pumpin an optimal fashion.

The foregoing is considered as illustrative only of the principles ofthe invention. Furthermore, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and operation shown anddescribed. While the preferred embodiment has been described, thedetails may be changed without departing from the invention, which isdefined by the claims.

1. A method for monitoring a centrifugal pump within a fluid flownetwork and relieving said pump of deleterious effects caused by anincreased pressure and/or temperature in said pump, said pumpcommunicating with a fluid release valve connected to a fluid conduit,said method comprising: selecting a sensor to monitor a variable of saidpump; providing a fluid control device; providing an electrical solenoidoperated valve having an inlet connected to said fluid conduit and anoutlet and a solenoid operated diaphragm, said diaphragm having a firstposition and a second position; providing a power supply; attaching saidsensor to said fluid conduit or said network; attaching said fluidcontrol device and said solenoid operated valve to said fluid conduit;forming an electrical circuit by attaching said sensor and the solenoidoperated valve to said power supply; and moving said diaphragm from saidfirst position to said position second position by completing saidelectrical circuit to the solenoid of said solenoid operated valve. 2.The method of claim 1 wherein said step of attaching said fluid controldevice and said solenoid operated valve further comprises attaching saidfluid control device and said solenoid operated valve to said fluidconduit at a distance of four inches or less to one another.
 3. Themethod according to claim 1 further comprising the steps of: selecting asecond sensor to monitor a second variable of said pump; and attachingsaid second sensor to said fluid conduit or said network.
 4. The methodof claim 1, wherein said step of moving said diaphragm results in allowsfluid flow through said solenoid operated valve.